[icebraining]

Plus you can take food with you if you need, and drinks from the airport past security, though those aren't necessarily cheaper.

[crtasm]

Take an empty bottle and get free water at some UK airports. I've not confirmed this personally yet

https://www.moneysavingexpert.com/travel/travel-tips#water

[icebraining]

I did this in Hamburg (technically I bought a bottle, but I drank it before boarding, so I refilled it before flight). But in my limited experience, these fountains are not common in EU airports.